In the past, certain rotary lawnmowers have incorporated a centrifugal clutch which interconnects the engine with the rotating blade. When the engine speed increases from idle to a predetermined value, the centrifugal clutch will move to an engaged position to interconnect the blade with the engine and cause the blade to rotate. On a decrease in engine speed, the clutch will disengage and, the blade will freely rotate to a stop. During this period of free rotation, there have been instances of injury to the operator, who, thinking the blade had stopped rotating, had reached under the housing.
To remedy this situation, brake mechanisms have been incorporated with the clutch, and in lawn mowers of this type, the brake is operated on disengagement of the clutch to prevent free rotation of the blade. Lawn mowers utilizing a clutch and brake mechanism have a dual operating cable system, with one cable serving to operate the throttle and a second cable serving to operate the brake.
Recently lawn mowers have been constructed with a spring loaded, throttle operating lever mounted on the upper end of the handle. The operating lever is spring biased to an idle position, and the engine speed is increased by moving the lever toward the full throttle position against the force of the spring. On release of the operating lever, the lever will automatically be returned to the idle position. To provide added safety and prevent accidental operation of the lever, a two-step actuation system has been incorporated with the operating lever. With systems of this type, the operating lever is locked in the idle position and the operator must initially release the lock and them move the operating lever to the full throttle position. With systems of this type, it takes two conscious movements on the part of the operator to increase the engine speed through operation of the lever.